This invention relates in general to charge transfer devices and in particular to charge transfer shift registers in which one section thereof is clocked at one frequency and another adjacent section thereof is clocked at another frequency.
In certain applications such as in ultrasound imaging apparatus wherein it is desirable to provide variable time delays in various signal channels, it is desirable to transfer charge from one charge transfer stage in a first charge transfer structure operated at one frequency directly into another charge transfer stage in a second charge transfer structure formed on the same substrate and clocked at a different frequency to provide a variable delay which is a function of the frequencies of the clocking voltages applied to the two structures. The transfer of charge from the first charge transfer structure directly into the second charge transfer structure presents a problem when the phases of the clocking voltages applied to the two structures are such as to prevent the transfer of charge directly from the last stage of the first charge transfer structure into the first stage of the second charge transfer structure. Such a condition causes charge to build up in the last cell of the first charge transfer structure and limits the dynamic range of the device.